Ceramic heater

ABSTRACT

An objective of the present invention is to provide a ceramic heater making it possible to heat an object to be heated, such as a silicon wafer, evenly. The ceramic heater of the present invention is a ceramic heater having and a resistance heating element formed on the surface of the ceramic substrate or inside the ceramic substrate, wherein: said ceramic heater is equipped with: a temperature-measuring means measuring the temperature of said ceramic substrate and an object to be heated; a control unit supplying electric power to said heating element; a memory unit memorizing the temperature data measured by said temperature-measuring means; and an operation unit calculating electric power required for said heating element from said temperature, said ceramic heater being constituted such that said heating element is divided into at least 2 or more circuits and different electric power is supplied to each of the circuits of said resistance heating element.

TECHNICAL FIELD

The present invention relates to a ceramic heater used mainly in thesemiconductor industry, for drying, sputtering and the like of thesemiconductor and the like, and particularly to a ceramic heater whereinthe temperature thereof can easily be controlled and the temperatureevenness of its wafer-heating face is superior.

BACKGROUND ART

A semiconductor product is produced through the steps of forming aphotosensitive resin as an etching resist on a silicon wafer andsubjecting the silicon wafer to etching, and the like steps.

This photosensitive resin is liquid, and is applied onto a surface ofthe silicon wafer, using a spin coater and the like. After theapplication, the resin has to be dried. Thus, the silicon wafersubjected to the application process is put on a heater and heated.

Hitherto, as a heater made of metal and used for such a purpose, aheater wherein heating elements are arranged on the back surface of analuminum plate is adopted.

SUMMARY OF THE INVENTION

However, such a heater made of metal has the following problems.

First, the thickness of the heater plate must be as thick as about 15 mmsince the heater is made of metal. This is because a bend, a strain andso on are generated due to thermal expansion resulting from heating sothat a silicon wafer put on the metal plate is damaged or inclined incase of a metal plate being thin. However, if the thickness of theheater plate is made thick, the heater becomes heavy and bulky.

Also, heating temperature is controlled by changing the voltage oramperage applied to the heating elements. However, since the metal plateis thick, the temperature of the heater plate does not follow the changein the voltage or amperage promptly. Thus, such a problem that thetemperature cannot be easily controlled is caused.

Thus, as suggested in JP Kokai Publication Hei 8-8247, there is atechnique suggested, wherein a nitride ceramic at which heating elementsare formed is used to perform temperature-control while measuring thetemperature near the heating elements.

However, when such a technique is used to heat a silicon wafer, aproblem that the silicon wafer is damaged by thermal shock resultingfrom a temperature-difference on the surface of the heater is caused.

Thus, the inventors made eager investigations on causes of the damage ofthe silicon wafer. As a result, the inventors have found out that theoccurrence of the damage of the silicon wafer, in spite of performingtemperature-control, is owing to the following fact: even if singletemperature control is conducted, it is difficult to make thetemperature of the heating face even and the temperature differencearises depending on the portion of the silicone wafer, thus the siliconwafer is damaged.

The inventors have also found out a new fact that such unevenness of thetemperature is significant in ceramics having a high thermalconductivity, such as nitride ceramic and carbide ceramic and the like.

Incidentally, JP Kokai Publication Hei 6-252055 proposes a controllingtechnique to control the temperature of the central portion higher thanthe temperature of the peripheral portion thereof, and JP KokaiPublication Sho 63-216283 proposes a controlling technique in which thecircuits of the heating element is divided. However, each of them is thetechnique to control the temperature according to the predeterminedschedule.

However, in the actual heating of the silicone wafer, a disturbanceoccurs in such a case that a silicone wafer with low temperature is putthereon Thus, with the above-mentioned technique wherein the schedule ofcontrolling the temperature is determined in advance, the temperaturecontrol is hard to be done in the case that unexpected temperaturechange occurs.

Thus, repeating further investigations, the inventors have found outthat by: dividing the above-mentioned resistance heating element to twoor more circuits and performing the temperature control by supplying thedifferent electric power based on the result of the temperaturemeasurement to conduct heating so as to reduce the temperaturedifference on the face for heating an object to be heated (hereinafter,referred to as heating face as well) can be made even, the wholetemperature of the object to be heated such as a semiconductor wafer andthe like is made even, the damage of the semiconductor wafer isprevented, and the temperature control can be successfully done even inthe case the unexpected temperature change occures, and have made thepresent invention which has, as the subject matter thereof, thefollowing contents.

That is, a ceramic heater of the first aspect of the present inventionis a ceramic heater comprising a ceramic substrate and a resistanceheating element formed on the surface of the ceramic substrate or insidethe ceramic substrate,

wherein: the ceramic heater is equipped with:

a temperature-measuring means measuring the temperature of the ceramicsubstrate or an object to be heated;

a control unit supplying electric power to the heating element;

a memory unit memorizing the temperature data measured by thetemperature-measuring means; and

an operation unit calculating electric power required for the heatingelement from the temperature data, the ceramic heater being constitutedsuch that the heating element is divided into at least 2 or morecircuits and different electric power is supplied to each of thecircuits.

A ceramic heater of the second aspect of the present invention is aceramic heater comprising a ceramic substrate and a resistance heatingelement formed on the surface of the ceramic substrate or inside theceramic substrate,

wherein: the ceramic heater is equipped with:

a temperature-measuring means measuring the temperature of the ceramicsubstrate or an object to be heated;

a power source supplying electric power to the heating element;

a control unit controlling the power source;

a memory unit memorizing the temperature data measured by thetemperature-measuring means; and

an operation unit calculating electric power required for the heatingelement from the temperature data;

the ceramic heater being constituted such that the heating element isdivided into at least 2 or more circuits and different electric power issupplied to each of the circuits.

In the first aspect and second aspect of the ceramic heater, thetemperature-measuring means is, preferably, a thermoviewer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a block figure that schematically shows an example of aceramic heater of the first aspect of the present invention, and FIG.1(b) is a partially enlarged sectional view of this ceramic heater.

FIG. 2 is a plane view that schematically shows an example of a ceramicheater of the first aspect of the present invention.

FIG. 3 is a block figure that schematically shows another example of aceramic heater of the first aspect of the present invention.

FIG. 4 is a graph showing temperature profiles of a ceramic heateraccording to Example 4.

FIG. 5 is a graph showing electric power (electric current) profiles ofa ceramic heater according to Example 4.

FIG. 6 is a block figure that schematically shows an example of aceramic heater of the second aspect of the present invention.

FIG. 7(a) is a schematic diagram that shows an image of data obtained bythe thermoviewer shown in FIG. 6; and (b) is a schematic diagram whichshows the state that the diagram shown in (a) is divided into pluralpixels, and the colors of respective pixels are subjected to themulti-level judgment and valued in multiple steps.

FIG. 8 is a graph showing the state of the temperature recovery of theceramic heater when a disturbance occurred on the surface of the ceramicsubstrate according to Example 4.

FIG. 9 is a graph showing electric power (electric current) profiles ofa ceramic heater according to Example 5.

FIG. 10 is a graph showing temperature profiles of a ceramic heateraccording to Example 5.

Explanation of symbols 10, 30, 50 a ceramic heater 11, 31, 51 a heaterplate 12, 32 a heating element 13, 33 a terminal pin 14, 34 a bottomedhole 15, 35 a through hole 19 a silicon wafer 11a, 31a, 51a awafer-heating face 11b, 31b, 51b a bottom face 16 a lifter pin 17, 37 athermocouple 18 a conductor-filled through hole 21, 41, 61, 610 a memoryunit 22, 42, 62, 620 an operation unit 23, 43, 63 a control unit 560 asupporting pin 600 a thermoviewer 630 a power source unit

DETAILED DISCLOSURE OF THE INVENTION

Firstly, the ceramic substrate of the first aspect of the presentinvention is explained.

The ceramic heater of the first aspect of the present invention is aceramic heater comprising a ceramic substrate and a resistance heatingelement formed on the surface of the ceramic substrate or inside theceramic substrate,

wherein: the ceramic heater is equipped with:

a temperature-measuring means measuring the temperature of the ceramicsubstrate or an object to be heated;

a control unit supplying electric power to the heating element;

a memory unit memorizing the temperature data measured by thetemperature-measuring means; and

an operation unit calculating electric power required for the heatingelement from the temperature data,

the ceramic heater being constituted such that the heating element isdivided into at least 2 or more circuits and different electric power issupplied to each of the circuits.

According to the above-mentioned ceramic heater of the first aspect ofthe present invention, the temperature control can be performed bychanging an electric power supplied to the heating element divided into2 or more circuit based on the measurement result of the temperature ofthe wafer-heating face or the temperature of the object to be heatedsuch as a semiconductor wafer and the like, thus the temperature of thewafer-heating face can be made even. Therefore, the whole temperature ofthe object to be heated can be made even and the damage on the siliconewafer can be prevented.

FIG. 1(a) is a block figure that schematically shows an example of aceramic heater of the first aspect of the present invention, and FIG.1(b) is a partially enlarged sectional view of the ceramic heater. FIG.2 is a plane view that schematically shows a heater portion whichconstitutes a ceramic heater shown in FIG. 1.

A heater plate 11 is formed into a disc form. Heating elements 12(12 x,12 y) are formed into a pattern of concentric circles inside the heaterplate 11 in order to heat a wafer-heating face 11 a of the heater plate11 in such a manner that the whole temperature of the wafer-heating face11 a thereof becomes even. As to these heating elements 12, twoconcentric circles near to each other, as one set, are connected intoone line. Terminal pins 13, which will be input/output terminals, areconnected to two ends thereof through a conductor-filled through hole18. The terminal pins 13 are fitted with sockets 20, and the sockets 20are connected to a control unit 23 having a power source.

Through holes 15 into which lifter pins 16 are inserted are formed inareas near the center. Further, bottomed holes 14 a to 14 i into whichthermocouples 17 as a temperature-measuring means (atemperature-measuring element) are inserted are also formed.

As shown in FIG. 1, in this ceramic heater 10, lifter pins 16 areinserted into the through holes 15. A silicon wafer 19 is put on thelifter pins 16. By moving the lifter pins 16 upwards or downwards, thesilicon wafer 19 can be delivered to a non-illustrated carrier machine,or the silicon wafer 19 can be received from the carrier machine.

Also, by the supporting pins 560 (reference to FIG. 6), the siliconwafer can be heated while being held at a given distance apart from thewafer-heating face. The distance thereof is preferably to be 50 to 5000μm.

Bottomed holes 14 are made, from the side of the bottom face 11 b, inthe heater plate 11. Thermocouples 17 are fixed to the bottoms of thebottomed holes 14. The thermocouples 17 are connected to a memory unit21 so that the temperatures of the respective thermocouples 17 aremeasured every given interval and then, the data can be memorized. Thismemory unit 21 is connected to a control unit 23 and an operation unit22. On the basis of the data memorized in the memory unit 21, theoperation unit 22 calculates a voltage value and so on which are usedfor the control. On the basis of this calculation, a certain voltage isapplied from the control unit 23 to the respective heating elements 12so that the temperature on a wafer-heating face 11 a can be made even.

The following will describe the operation of the ceramic heater 10 ofthe present invention.

First, the control unit 23 is operated so that an electric power issupplied to the ceramic heater 10. As a result, the temperature of theheater plate 11 itself rises, but the surface temperature of theperipheral portion thereof becomes slightly low.

The data measured by the thermocouples 17 is once stored in the memoryunit 21. Next, the temperature data is sent to the operation unit 22. Inthe operation unit 22, temperature-differences ΔT: among each measuredpoint; or the temperature-difference from the given value are calculatedand further data ΔW necessary for making the temperature on thewafer-heating face 11 a even are calculated.

For example, in the case that the temperature-difference ΔT is generatedbetween the heating element 12 x and the heating element 12 y, and ifthe temperature of the heating element 12 x is lower, operations toobtain electric power data ΔW for making the ΔT to zero are run, thisdata is transmitted to the control unit 23 and an electric power basedon this data is supplied to the heating element 12 x to raise thetemperature thereof. Regarding the algorithm for calculating theelectric power, a method for calculating the electric power necessaryfor the rise in the temperature by utilizing the specific heat of theheater plate 11 and the weight of the heated area is most simple. Acorrection coefficient originating from the pattern of the heatingelements may be considered together with these factors. Alternatively, atemperature-rising test is beforehand performed on a specific heatingelement pattern, and functions among a temperature-measuring position, asupplying electric power and temperature are beforehand obtained. Fromthese functions, the supplying electric power may be calculated. Theapplying voltage and time corresponding to the electric power calculatedin the operation unit 22 are transmitted to the control unit 23. On thebasis of these values, electric powers are supplied to the respectiveheating elements 12 by the control unit 23.

That is, the ceramic heater of the first aspect of the present inventionhas the operation unit 22. Thus, even in case that an expectedtemperature change occurred, the electric power for making thetemperature even can be calculated, and a practical temperature controlcan be achieved.

Next, respective parts which constitute the ceramic heater of the firstaspect of the present invention are explained.

In the ceramic heater 10, the thickness of the heater plate 11 ispreferably 0.5 to 5 mm. If the thickness is thinner than 0.5 mm, thestrength thereof is lowered so that the heater plate is easily damaged.On the other hand, if the thickness is thicker than 5 mm, heat is noteasily conducted so that heating efficiency is lowered.

The ceramic constituting the ceramic heater 10 is desirably a nitrideceramic or a carbide ceramic.

A nitride ceramic or a carbide ceramic has a smaller thermal expansioncoefficient than metals and far higher mechanical strength than metals.Thus, even if the thickness of a ceramic plate 11 is made thin, theheater plate is not warped or distorted by heating. As a result, theheater plate can be made thin and light. Further, since the thermalconductivity of the heater plate 11 is high and the heater plate itselfis thin, the surface temperature of the heater plate follows a change inthe temperature of the heating element promptly. In other words, bychanging voltage or amperage to change the temperature of the heatingelement 12, the surface temperature of the heater plate (the temperatureof the wafer-heating face) can be controlled.

Examples of the nitride ceramic include aluminum nitride, siliconnitride, boron nitride and titanium nitride and the like. These may beused alone or in combination of two or more.

Examples of the carbide ceramic include silicon carbide, zirconiumcarbide, titanium carbide, tantalum carbide and tungsten carbide and thelike. These may be used alone or in combination of two or more.

Among these, aluminum nitride is most preferred. The reasons for thisare as follows: its thermal conductivity is highest, that is, 180 W/m·Kand aluminum nitride has superior temperature-following property, on theother hand, since aluminum nitride easily causes unevenness oftemperature distribution, it is necessary to adopt thetemperature-measuring means as shown in the present invention.

In the ceramic heater 10 of the present invention it is desired that:,bottomed holes 14 a to 14 i (hereinafter, may be referred to simply asbottomed holes 14, as well) are made, from the opposite side (bottomface) of a wafer-heating face 11 a for putting an object to be heated,toward the wafer-heating face 11 a; the bottom of the bottomed holes 14is formed relatively nearer to the wafer-heating face 11 a than to theheating elements 12; and a temperature-measuring means is set up in thisbottomed hole 14. (reference to FIG. 1)

The distance L between the bottom of the bottomed holes 14 and thewafer-heating face 11 a is desirably from 0.1 mm to ½ of the thicknessof the ceramic substrate. (reference to FIG 1(b))

Thus, a place for temperature-measurement is nearer to a wafer-heatingface 11 a than to the heating element 12. Therefore, the temperature ofthe silicone wafer can be more correctly measured. This correctlymeasured result of the temperature is memorized in the memory unit 21,and then an electric voltage which is going to be supplied to theheating element 12 in order to perform even heating is calculated in theoperation unit 22 on the basis of the temperature data memorized in thememory unit 21. On the basis of the calculated result, a voltage forcontrol is applied to the heating element 12 by the control unit 23,thus the temperature of the wafer-heating face becomes even. Therefore,the whole of the object to be heated such as a silicon wafer and thelike can be evenly heated.

If the distance between the bottom of the bottomed holes 14 and thewafer-heating face 11 a is below 0.1 mm, heat is radiated so that atemperature distribution is produced on the wafer-heating face 11 a. Onthe other hand, if the distance is over ½ of the thickness thereof, theinfluence of the temperature of the heating elements over the controlapt to be significant so that a temperature distribution is produced onthe wafer-heating face 11 a as well.

The diameter of the bottomed holes 14 is desirably 0.3 to 0.5 mm. If thediameter is too large, the heat radiant property becomes too large. Ifthe diameter is too small, the processability becomes poor so that thedistance between the wafer-heating face 11 a and the bottomed holescannot be made even.

As shown in FIG. 2, the bottomed holes 14 a to 14 i are desirablyarranged into a cross form, and symmetrically with respect to the centerof the heater plate 11. Such arrangement makes it possible to measurethe whole temperature of the wafer-heating face.

Examples of the temperature-measuring means include a thermocouple and aplatinum temperature-measuring resistance, a thermistor and the like.Besides, the temperature-measuring means using an optical means such asa thermoviewer and the like can be listed.

In case that the above-mentioned thermoviewer is used, the precision ofthe temperature control of the object to be heated improves since thetemperature on the surface of the ceramic substrate can be measured aswell as the surface temperature of the object to be heated such as asemiconductor wafer and the like can be directly measured.

The temperature control using the above-mentioned thermoviewer is to beexplained in detail in the explanation of the ceramic heater of thesecond aspect of the present invention.

Examples of the thermocouple include K, R, B, S, E, J and T typethermocouples and the like, as described in JIS-C-1602 (1980). Amongthese, the K type thermocouple is preferred.

Desirably, the size of the connecting portion of the thermocouple isequal to or more than the diameter of its strand wire, and is 0.5 mm orless. If the connecting portion is large, the thermal capacity is largeso that the response becomes poor. Incidentally, making the size thereofsmaller than the diameter of the strand wire is difficult.

In case that the temperature measuring element is used, thetemperature-measuring element may be bonded to the bottoms of thebottomed holes 14, using gold solder, silver solder and the like. Thetemperature-measuring elements may be inserted into the bottomed holes14 and then, may be sealed with a heat resistant resin. The both mannersmay be used together.

Examples of the heat resistant resin may be thermosetting resins, inparticular, epoxy, polyimide, bismaleimide-triazine and the like. Theseresins may be used alone or in combination of two or more.

The gold solder is desirably at least one selected from an alloy of 37to 80.5% by weight of Au-63 to 19.5% by weight of Cu, an alloy of 81.5to 82.5% by weight of Au-18.5 to 17.5% by weight of Ni. These have amelting temperature of 900° C. or higher and are not easily melted evenat a high temperature range.

The silver solder that can be used may be, for example, a Ag—Cu type.

As shown in FIG. 2, the heating elements 12 are desirably divided intoat least two or more circuits, and more desirably divided into 2 to 10circuits. By the division into the circuits, each electric powersupplied to the respective circuits can be controlled to change thecalorific value thereof so that the temperature of the wafer-heatingface 11 a can be adjusted.

Examples of the pattern of the heating elements 12 include theconcentric circuits shown in FIG. 2, a spiral, eccentrics, and windinglines and the like.

In the present invention, the heating elements may be formed on thesurface (bottom face) of the heater plate and may be formed inside theheater plate.

In case of forming a heating element on the surface of the heater plate11, adopting the following method is preferred: a method in which aconductor containing paste containing metal particles is applied to thesurface of the heater plate 11 to form a conductor containing pastelayer having a given pattern, and then this is fired to sinter the metalparticles on the surface of the heater plate 11. Incidentally, thesintering of the metal is sufficient if the metal particles are meltedand adhered to each other; and the metal particles and the ceramic aremelted and adhered to each other.

When the heating elements are formed on the surface of the heater plate11, the thickness of the heating elements is preferably 1 to 30 μm andmore preferably 1 to 10 μm. When the heating elements are formed insidethe heater plate 11, the thickness thereof is preferably 1 to 50 μm.

When the heating elements are formed on the surface of the heater plate11, the width of the heating elements is preferably 0.1 to 20 mm andmore preferably 0.1 to 5 mm. When the heating elements are formed insidethe heater plate 11, the width of the heating elements is preferably 5to 20 μm.

The resistance value of the heating elements can be changed dependentlyon their width or thickness. The above-mentioned ranges are however mostpractical. The resistance value becomes larger as the heating elementsbecome thinner and narrower. The thickness and the width of the heatingelements become larger in the case that the heating elements are formedinside the heater plate 11. The reason for this is as follows:

when the heating elements are formed inside, the distance between thewafer-heating face and the heating elements becomes short so that theevenness of the temperature on the surface becomes poor, thus, it isnecessary to make the width of the heating elements themselves large;

also, when the heating elements are formed inside, it is unnecessary toconsider the adhesiveness to any ceramic, for example, a nitrideceramic. Therefore, it is possible to use a high melting point metalsuch as tungsten or molybdenum, or a carbide of tungsten, molybdenum andthe like. Thus, it becomes possible to make the resistance value thereofhigh. Therefore, the thickness itself may be made large in order toprevent disconnection and so on. For these reasons, the heating elementsdesirably have the above-mentioned thickness and width.

By setting the position where the heating element is formed in this way,heat generated from the heating element diffuses all over the heaterplate while the heat is conducted. As a result, the temperaturedistribution on the surface for heating an object to be heated (asilicon wafer) is made even so that the temperatures at respectiveportions of the object to be heated are made even.

The heating elements may have a rectangular section or an ellipticalsection. But, they desirably have a flat section. This is because: incase of the flat section, heat is more easily radiated toward thewafer-heating face. Thus, a temperature distribution on thewafer-heating face is not easily generated.

The aspect ratio (the width of the heating element/the thickness of theheating element) of the section is desirably 10 to 5000.

Adjustment thereof into this range makes it possible to increase theresistance value of the heating elements and keep the evenness of thetemperature on the wafer-heating face.

In the case that the thickness of the heating elements is made constant:if the aspect ratio is smaller than the above-mentioned range, theamount of heat conduction toward the wafer-heating face of the heaterplate 11 becomes small so that a thermal distribution similar to thepattern of the heating elements is generated on the wafer-heating face;on the other hand, if the aspect ratio is too large, the temperature ofthe portions just above the centers of the heating elements becomes highso that a thermal distribution similar to the pattern of the heatingelements is also generated on the wafer-heating face. Accordingly, iftemperature distribution is considered, the aspect ratio of the sectionis preferably 10 to 5000.

When the heating elements are formed on the surface of the heater plate11, the aspect ratio is desirably 10 to 200. When the heating elementsare formed inside the heater plate 11, the aspect ratio is desirably 200to 5000.

The aspect ratio is set larger in the case that the heating elements areformed inside the heater plate 11. This is based on the followingreason. If the heating elements are formed inside, the distance betweenthe wafer-heating face and the heating elements becomes short so thattemperature evenness on the surface becomes poor. It is thereforenecessary to make the heating elements themselves flat.

The position where the heating elements of the present invention areformed to be biased inside the heater plate 11 is desirably at aposition near the bottom face 11 b which is on the opposite side to thewafer-heating face 11 a of the heater plate 11, and at a positionexceeds 50% and up to 99% of the distance from a wafer-heating face 11 ato the bottom face 11 b.

If the value is 50% or less, the position is too near to thewafer-heating face so that temperature-dispersion is caused. Conversely,if the value is over 99%, the heater plate 11 itself warps to damage asilicon wafer.

In the case that the heating elements are arranged inside the heaterplate 11, plural heating element formed layers may be formed. In thiscase, the patterns of the respective layers are preferably disposed inmutually complementary relation so that, when viewed from the positionabove the wafer-heating face, the patterns are formed in all areas. Apreferred example of such a structure having a staggered arrangement.

The conductor containing paste is not particularly limited, and ispreferably a paste comprising not only metal particles or a conductiveceramic for keeping electrical conductivity but also a resin, a solvent,a thickener and so on.

The metal particles are preferably of, for example, a noble metal (gold,silver, platinum or palladium), lead, tungsten, molybdenum, nickel andthe like. These may be used alone or in combination of two or more.These metals are not relatively easily oxidized, and have a resistancevalue sufficient for generating heat.

Examples of the conductive ceramic include carbides of tungsten,molybdenum and the like. These may be used alone or in combination oftwo or more.

The particle diameter of these metal particles or the conductive ceramicis preferably 0.1 to 100 μm. If the particle diameter is too fine, thatis, below 0.1 μm, they are easily oxidized. On the other hand, if theparticle diameter is over 100 μm, they are not easily sintered so thatthe resistance value becomes large.

The shape of the metal particles may be spherical or scaly. When thesemetal particles are used, they may be a mixture of spherical particlesand scaly particles.

In the case that the metal particles are scaly or a mixture of sphericalparticles and scaly particles, metal oxides between the metal particlesare easily retained and adhesiveness between the heating elements andthe nitride ceramic and the like are made sure. Moreover, the resistancevalue can be made large. Thus, this case is profitable.

Examples of the resin used in the conductor containing paste includeepoxy resins, phenol resins and the like. Examples of the solvent areisopropyl alcohol and the like. Examples of the thickener are celluloseand the like.

It is desired to add a metal oxide to the metal particles in theconductor containing paste and make the heating element into a sinteredbody of the metal particles and the metal oxide, as described above. Bysintering the metal oxide together with the metal particles in this way,the nitride ceramic or the carbide ceramic, which is the heater plate,can be closely adhered to the metal particles.

The reason why the adhesiveness to the nitride ceramic or the carbideceramic is improved by mixing the metal oxide is unclear, but would bebased on the following. The surface of the metal particles, or thesurface of the nitride ceramic or the carbide ceramic is slightlyoxidized so that an oxidized film is formed thereon. Pieces of theseoxidized films are sintered and integrated with each other through themetal oxide so that the metal particles and the nitride ceramic or thecarbide ceramic are closely adhered to each other.

A preferred example of the metal oxide is at least one selected from thegroup consisting of lead oxide, zinc oxide, silica, boron oxide (B₂O₃),alumina, yttria, and titania.

These oxides make it possible to improve adhesiveness between the metalparticles and the nitride ceramic or the carbide ceramic withoutincreasing the resistance value of the heating elements.

When the total amount of the above mentioned metal oxides is set to 100parts by weight, the weight ratio of the above mentioned lead oxide,zinc oxide, silica, boron oxide (B₂O₃), alumina, yttria and titania isas follows: lead oxide: 1 to 10, silica: 1 to 30, boron oxide: 5 to 50,zinc oxide: 20 to 70, alumina: 1 to 10, yttria: 1 to 50 and titania: 1to 50. The weight ratio is preferably adjusted within the scope that thetotal thereof is not over 100 parts by weight.

By adjusting the amounts of these oxides within these ranges, theadhesiveness to the nitride ceramic can be particularly improved.

The addition amount of the metal oxides to the metal particles ispreferably 0.1% by weight or more and less than 10% by weight. The arearesistivity when the conductor containing paste having such a structureis used to form the heating elements is preferably from 1 mΩ/□ to 45Ω/□. If the area resistivity is over 45 mΩ/□, the calorific value for anapplied voltage becomes too small so that, in the ceramic plate 11wherein heating elements are set on its surface, its calorific value isnot easily controlled. If the addition amount of the metal oxides is 10%by weight or more, the area resistivity exceeds 50 mΩ/□. As a result,the calorific value becomes too large so that temperature-controlbecomes difficult and the evenness of the temperature distributiondeteriorates.

In case that the heating elements are formed on the surface of theheater plate 11, a metal covering layer 38 (reference to FIG. 3) ispreferably formed on the surface of the heating elements. The metalcovering layer prevents a change in the resistance value based onoxidization of the inner metal sintered body. The thickness of theformed metal covering layer is preferably from 0.1 to 10 μm.

The metal used when the metal covering layer is formed is notparticularly limited if the metal is a metal which is non-oxidizable.Specific examples thereof include gold, silver, palladium, platinum,nickel and the like. These may be used alone or in combination of two ormore. Among these metals, nickel is preferred.

In the heating element, a terminal for connecting to a power source isnecessary. This terminal is fixed to the heating element through solder.Nickel prevents solder from being thermally diffused An example of theconnecting terminal is a terminal pin 13 made of Kovar.

In the case that the heating elements are formed inside the heater plate11, no coating is necessary since the surface of the heating elements isnot oxidized. In the case that the heating elements are formed insidethe heater plate 11, a part of the heating elements may be exposed inthe surface. It is allowable that conductor filled through holes forconnecting to the heating elements are made in portions for theterminals, and terminals are connected and fixed to the conductor filledthrough holes.

In the case that the connecting terminals are connected, an alloy suchas silver-lead, lead-tin or bismuth-tin can be used as a solder. Thethickness of the solder layer is desirably from 0.1 to 50 μm. This isbecause this range is a range sufficient for maintaining connectionbased on the solder.

Next, the process for producing a ceramic heater of the first aspect ofthe present invention is explained. The following will describe theprocess for producing a ceramic heater 10 wherein the heating elementsare formed inside the heater plate (reference to FIG. 1 to 2).

(1) Step of Manufacturing the Heater Plate

First, powder of a nitride ceramic or a carbide ceramic is mixed with abinder, a solvent and so on to prepare a paste. This is used to form agreen sheet.

As the above-mentioned ceramic powder, aluminum nitride, silicon carbideand the like can be used. If necessary, a sintering aid such as yttriamay be added.

As the binder, desirable is at least one selected from an acrylicbinder, ethylcellulose, butylcellosolve, and polyvinyl alcohol.

As the solvent, desirable is at least one selected from α-terpineol andglycol.

A paste obtained by mixing these is formed into a sheet form by thedoctor blade process, to form a green sheet.

The thickness of the green sheet is preferably 0.1 to 5 mm.

Next, the following are made in the resultant green sheet if necessary:portions which will be through holes into which lifter pins forsupporting a silicon wafer are inserted; portions which will be bottomedholes in which temperature-measuring elements such as thermocouples areburied; portions which will be conductor filled through holes forconnecting the heating elements to external terminal pins; and so on.After a green sheet lamination that will be described later is formed,the above-mentioned processing may be performed.

(2) Step of Printing a Conductor Containing Paste on the Green Sheet

A metal paste or a conductor containing paste containing an electricallyconductive ceramic is printed on the green sheet.

This conductor containing paste contains metal particles or conductiveceramic particles.

The average particle diameter of tungsten particles or molybdenumparticles is preferably 0.1 to 5 μm. If the average particle is below0.1 μm or over 5 μm, the conductor containing paste is not easilyprinted.

Such a conductor containing paste may be a composition (paste) obtainedby mixing, for example, 85 to 87 parts by weight of the metal particlesor the electrically conductive ceramic particles; 1.5 to 10 parts byweight of at least one kind of binder selected from acrylic binders,ethylcellulose, butylcellosolve and polyvinyl alcohol; and 1.5 to 10parts by weight of at least one solvent selected from α-terpineol andglycol.

(3) Step of Laminating the Green Sheets

Green sheets on which no conductor containing paste is printed arelaminated on the upper and lower sides of the green sheet on which theconductor containing paste is printed.

At this time, the number of the green sheet laminated on the upper sideis made larger than that of the green sheet laminated on the lower sideto cause the position where the heating elements are formed to be biasedtoward the bottom face.

Specifically, the number of the green sheets laminated on the upper sideis preferably 20 to 50, and that of the green sheets laminated on thelower side is preferably 5 to 20.

(4) Step of Firing the Green Sheet Lamination

The green sheet lamination is heated and pressed to sinter the ceramicparticles and the inner conductor containing paste in the green sheets.

The heating temperature is preferably 1000 to 2000° C., and the pressingpressure is preferably 10 to 20 MPa. The heating is performed in theatmosphere of an inert gas. As the inert gas, argon, nitrogen and thelike can be used.

After the firing, bottomed holes 14 into which temperature-measuringelements will be inserted may be made. The bottomed holes 14 can be madeby blast treatment such as sandblast after surface-polishing. Terminalpins 13 are connected to the conductor filled through holes forconnecting to the inner heating elements, and then the portion is heatedfor reflowing. The heating temperature is suitably 200 to 500° C.

Furthermore, thermocouples and the like as temperature-measuringelements are inserted and set up with silver solder, gold solder and thelike, and then the holes are sealed with a heat-resistant resin such aspolyimide and the like to finish the manufacture of the ceramic heater.

FIG. 3 is a block figure that schematically shows another example of aceramic heater of the present invention.

In a ceramic heater 30 shown in FIG. 3, heating elements 32 (32 x, 32 y)are formed on a bottom face 31 b of a heater plate 31, and metalcovering layers 38 are formed around the heating elements 32.

A terminal pin 33 is connected and fixed to the heating elements throughthe metal covering layer 38. The terminal pin 33 is fitted with a socket40. This socket 40 is connected to a control unit 43 having a powersource. Other parts are formed in the same way as in the ceramic heatershown in FIG. 2.

That is, the shape of the heater plate 31 is similar to the heater plate11 shown in FIG. 1 which is in a disc shape. Also, planar view of thepattern of the heating element 32 formed on the heater plate 11, theposition at which the heating elements are formed and the shape andformed position of the bottomed holes 34 are similar to the ceramicheater 10 shown in FIG. 2.

Next, the operation of the ceramic heater 30 shown in FIG. 3 isexplained.

The ceramic heater 30 shown in FIG. 3 operates in the same way as theceramic heater 10 shown in FIG. 1 to 2. The temperatures ofthermocouples 32 x, 32 y are measured every given interval. Thus, thedata is memorized in the memory unit 41. From the data, a voltage valueand so on for control are calculated in the operation unit 42. On thebasis of these, a certain amount of voltage is applied from the controlunit 43 to the heating elements 32 x, 32 y so that the whole temperatureof the wafer-heating face 31 a of the ceramic heater 30 can be madeeven.

Next, the process for producing a ceramic heater 30 shown in FIG. 3 isexplained.

(1) Step of Forming the Heater Plate

If necessary, a sintering aid such as yttria, a binder and so on areblended with powder of the above-mentioned nitride ceramic, such asaluminumnitride, or a carbide ceramic to prepare a slurry. Thereafter,this slurry is made into a granular form by spray drying and the like.The granule is put into a mold and pressed to be formed into a plateform and the like form. Thus, a raw formed body(green) is formed.

Next, portions that will be the through holes 35 into which lifer pinsfor supporting a silicon wafer are inserted; and portions that will bethe bottomed holes 34 in which temperature-measuring elements such asthermocouples are buried, are formed in the raw formed body by drilling,blast treatment and the like if necessary.

Next, this raw formed body is heated and fired to be sintered. Thus, aplate made of the ceramic is produced. Thereafter, the plate is madeinto a given shape to produce the heater plate 31. The shape of the rawformed body may be such a shape that the sintered body can be used as itis. By heating and firing the raw formed body under pressure, the heaterplate 31 having no pores can be produced. It is sufficient that theheating and the firing are performed at sintering temperature or higher.The firing temperature is 1000 to 2500° C. for nitride ceramics orcarbide ceramics.

Incidentally, the through holes 35 and the bottomed holes 34 may beformed after manufacturing a heater plate 31. In this case, formation isdesirably conducted by the sand blasting method using SiC particles andthe like.

(2) Step of Printing a Conductor Containing Paste on the Heater Plate

A conductor containing paste is generally a fluid comprising metalparticles, a resin and a solvent, and has a high viscosity. Thisconductor containing paste is printed in portions where heating elementsare to be arranged, by screen printing and the like, to form a conductorcontaining paste layer. Since it is necessary that the heating elementsmake the whole temperature of the heater plate even, the conductorcontaining paste is desirably printed into a pattern of concentriccircles, as shown in FIG. 2.

The conductor containing paste layer is desirably formed in the mannerthat a section of the heating elements 32 after the firing isrectangular and flat shape.

(3) Firing of the Conductor Containing Paste

The conductor containing paste layer printed on the bottom face of theheater plate 31 is heated and fired to remove the resin and the solventand sinter the metal particles. Thus, the metal particles are sinteredand baked onto the bottom face of the heater plate 31 to form theheating elements 32. The heating and firing temperature is preferably500 to 1000° C.

If the above-mentioned metal oxides are added to the conductorcontaining paste, the metal particles, the heater plate and the metaloxides are sintered to be integrated with each other. Thus, theadhesiveness between the heating elements 32 and the heater plate 31 isimproved.

(4) Forming a Metal Covering Layer

A metal covering layer is desirably deposited on the surface of theheating elements 32. The metal covering layer can be formed byelectroplating, electroless plating, sputtering and the like. From theviewpoint of mass-productivity, electroless plating is optimal.

(5) Fitting of Terminals and so on

Terminals (terminal pins 33) for connecting to a power source are fittedup to ends of the pattern of the heating elements 32 with solder.Thermocouples are fixed to the bottomed holes 34 with silver solder,gold solder and the like. The bottomed holes are sealed with a heatresistant resin such as a polyimide and the like to finish themanufacture of the ceramic heater 30.

Incidentally, as to the ceramic heater of the present invention,electrostatic electrodes may be arranged to make an electrostatic chuck,or a chuck top conductor layer may be arranged thereon to make a waferprober.

Next, the ceramic heater of the second aspect of the present inventionwill be described.

The second aspect of the present invention is a ceramic heatercomprising a ceramic substrate and a resistance heating element formedon the surface of the ceramic substrate or inside the ceramic substrate,

wherein: the ceramic heater is equipped with:

a temperature-measuring means measuring the temperature of the ceramicsubstrate or an object to be heated;

a power source supplying electric power to the heating element;

a control unit controlling the power source;

a memory unit memorizing the temperature data measured by thetemperature-measuring means; and

an operation unit calculating electric power required for the heatingelement from the temperature data;

the ceramic heater being constituted such that the heating element isdivided into at least 2 or more circuits and different electric power issupplied to each of the circuits.

According to the ceramic heater of the second aspect of the presentinvention, similarly to the ceramic heater of the first aspect of thepresent invention, the temperature control can be performed by changingan electric power supplied to the heating element divided into 2 or morecircuit based on the measurement result of the temperature of thewafer-heating face or the temperature of the object to be heated, thusthe whole temperature of the wafer-heating face can be made even.Therefore, the temperature of the object to be heated can be made evenand the damage on the silicone wafer can be prevented.

FIG. 6 is a block figure that schematically shows an example of aceramic heater of the second aspect of the present invention.

In the ceramic heater 50 shown in FIG. 6, except that supporting pinswhich supports a silicon wafer 19 in condition is that the siliconewafer is held at a given distance apart from the wafer-heating face 51 aare formed, the peripheral portion of the heating plate 51 isconstituted similarly to the ceramic heater 30 shown in FIG. 3.

In the ceramic heater 50, a thermoviewer 600 for measureing the surfacetemperature of a silicone wafer 19 or an object to be heated is equippedabove the silicone wafer 19. The thermoviewer 600 is also connected to amemory unit 610. This memory unit 610 is connected to an operation unit620 as well as being connected to a memory unit 61. Furthermore, thecontrol unit 63 and the power source unit 630 are not integrated butseparately equipped. The memory unit 61 is connected to the operationunit 62 and the control unit 63, similarly to the ceramic heater 30shown in FIG. 3.

The memory unit 610 play a role of memorizing an image data obtainedfrom the thermoviewer 600, as well as provisionally memorizing atemperature data obtained by performing image-processing based on theimage data at the operation unit 620.

A memory unit 61 receives a temperature- measurement data as well asmemorizing the data for performing other controls. The operation unit 62performs an operation for control based on the temperature-measurementdata and the like.

That is, in the ceramic heater shown in FIG. 6. The memory unit isdivided into: a memory unit 610 for memorizing exclusively the imagedata obtained from the thermoviewer 600; and the memory unit 61 formemorizing the data for control such as the temperature-measurement dataand the like. The operation unit is also divided into: an operation unit620 for performing exclusively an operation of the image data obtainedfrom the thermoviewer 600; and an operation unit 62 for controlling theheater. However, the memory unit 610 and the memory unit 61 may beintegrated into one memory unit, and also, the operation unit 620 andthe operation unit 62 may be integrated into one operation unit.Further, the control unit 63 and the power source unit 630 may beintegrated.

The following will describe the action of the above-mentioned ceramicheater 50 shown in FIG. 6.

In the ceramic heater 50, a thermoviewer 600 is equipped as atemperature measuring means and shoots the surface of the silicone wafer19 or the heater plate 51, and then transmits the optical data as wellas the image to the memory unit 610. The data stored in the memory unit610 is sent to the operation unit 620, and then subjected to the imageprocessing. In the image processing, the image optically classified incolor as shown in FIG. 7(a) is sectioned into plural pixels and then thecolors of respective pixels are subjected to the multi-level judgmentand valued in multiple steps as shown in FIG. 7(b).

In the ceramic heater 50, the control is conducted in condition that thecircuit of the heating elements is divided into 2 or more. Thus, aplurality of temperature controlled areas exist. The temperature T ofeach temperature controlled area is obtained either: by regarding thevalue obtained from the multi-level judgment at a particular point A asthe representative value; or by averaging each value obtained from themulti-level judgment at the respective temperature controlled areas.Then, the temperatures of the each temperature controlled area is storedin the memory unit 610 again.

The temperature data T stored in the memory unit 610 is transmitted tothe memory unit 61 for the control. Then, for instance, the differencebetween the temperature T of temperature controlled area and the desiredtemperature t; or temperature-differences ΔT among respectivetemperature controlled areas are calculated and further data ΔWnecessary for making ΔT into 0 are calculated, and then transmitted tothe control unit 63. On the basis of these values, electric powers aresupplied to the respective heating elements so that the temperaturerises so as to make the temperature of the wafer-heating face or anobject to be heated even.

It is apparent that, in the second aspect of the present invention, athermocouples and the like may be used as the temperature measurementmeans.

Similarly to the ceramic heater as shown in FIG. 3, the ceramic heater50 shown in FIG. 6 is assembled in the following manner that: aftermanufacturing the ceramic plate 31, the supporting pins 560 are equippedby processing the heater plate 31; the thermoviewer and the like asshown in FIG. 6 are equipped thereto; and then, wirings to a memory unit61, 610, the operation unit 62, 620 and the like are furnished.

In the ceramic heater 50 as shown in FIG. 6, a thermoviewer is used asthe temperature measurement means. Thus, the temperature control of thewafer-heating face of the heater plate and the object to be heated canbe conducted by the area-temperature control. In this way, the precisionof the temperature control is improved compared to the case ofconducting a point-temperature control using a temperature-measuringelement. Also, even in case that unexpected temperature change occurs,the temperature thereof can be recovered to the original temperature byimmediately coping with it. Thus, practical temperature control can berealized.

As mentioned above, the ceramic heater of the present invention has beenexplained. Incidentally, the ceramic substrate may be made to anelectrostatic chuck by arranging a resistance heating element on thesurface thereof or inside thereof, as well as arranging an electrostaticchuck inside thereof.

Also, the ceramic substrate may be made to a wafer prober by arranging aresistance heating element on the surface thereof or inside thereof aswell as arranging a chuck top conductor layer on the surface thereof,and further arranging a guard electrode and a ground electrode insidethereof.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detailed hereinafter.

(Example 1)

Manufacture of a Ceramic Heater made of Aluminum Nitride (reference toFIG. 3)

-   (1) A composition made of 100 parts by weight of aluminum nitride    powder (average particle diameter: 1.1 μm), 4 parts by weight of    yttria (average particle diameter: 0.4 μm), 12 parts by weight of an    acrylic binder and an alcohol was subjected to spray-drying to make    granular powder.-   (2) Next, this granular powder was put into a mold and formed into a    flat plate form to obtain a raw formed body (green).-   (3) The raw formed body subjected to the above-mentioned working    treatment was hot-pressed at 1800° C. and a pressure of 20 MPa to    obtain a nitride aluminum plate having a thickness of 3 mm.

Next, this plate was cut out into a disk having a diameter of 210 mm toobtain a plate (heater plate) 31 made of the ceramic.

This raw formed body was drilled to form: portions for through holes 35,into which lifter pins for the silicon wafer are inserted; and portions(diameter: 1.1 mm, and depth: 2 mm) for bottomed holes 34, in whichthermocouples are buried.

-   (4) A conductor containing paste was printed on the heater plate 31    obtained in the step (3) by screen printing. The pattern of the    printing was made to a pattern of concentric circles as shown in    FIG. 2.

This conductor containing paste was a silver-lead paste and containing7.5 parts by weight of metal oxides comprising lead oxide (5% byweight), zinc oxide (55% by weight), silica (10% by weight), boron oxide(25% by weight) and alumina (5% by weight) per 100 parts by weight ofsilver. The silver particles had an average particle diameter of 4.5 μm,and were scaly.

-   (5) Next, the heater plate 31 on which the conductor containing    paste was printed was heated and fired at 780° C. to sinter silver    and lead in the conductor containing paste and bake them onto the    heater plate 31. Thus, heating elements 32 were formed. The    silver-lead heating elements 32 had a thickness of 5 μm, a width of    2.4 mm and a area resistivity of 7.7 mΩ/□.-   (6) The heater plate 31 formed in the step (5) was immersed into an    electroless nickel plating bath comprising an aqueous solution    containing 80 g/L of nickel sulfate, 24 g/L of sodium hypophosphite,    12 g/L of sodium acetate, 8 g/L of boric acid, and 6 g/L of ammonium    chloride to precipitate a metal covering layer (nickel layer) 38    having a thickness of 1 μm on the surface of the silver-lead heating    elements 32.-   (7) A silver-lead solder paste (made by Tanaka Kikinzoku Kogyo CO.)    was printed by screen printing on portions to which terminal for    attaining connection to a power source were attached, to form a    solder layer.

Next, terminal pins 33 made of Kovar were put on the solder layer andheated at 420° C. for reflowing to attach the terminal pins 33 onto thesurface of the heating elements 32.

-   (8) Next, thermocouples for temperature-control were fitted in the    bottomed holes 34 and then they were fixed by embedding a ceramic    adhesive agent (made by Toagosei Co., Ltd., Aron ceramic) to obtain    a ceramic heater 30.    (Example 2)    Manufacture of a Ceramic Heater made of Silicon Carbide

A ceramic heater made of silicon carbide was manufactured in the sameway as in Example 1 except that silicon carbide having an averageparticle diameter of 1.0 μm was used, sintering temperature was set to1900° C., and the surface of the resultant heater plate was fired at1500° C. for 2 hours to form a SiO₂ layer having a thickness of 1 μm onthe surface.

(Example 3)

Manufacture of a Ceramic Heater having Heating Elements inside thereof.(FIGS. 1 to 2)

-   (1) A paste obtained by mixing aluminum nitride powder (made by    Tokuyama Corp., average particle diameter: 1.1 μm), 4 parts by    weight of yttria (average particle diameter: 0.4 μm), 11.5 parts by    weight of an acrylic binder, 0.5 part by weight of a dispersant, and    53 parts by weight of alcohols comprising 1-butanol and ethanol was    formed into a green sheet having a thickness of 0.47 μm by the    doctor blade process.-   (2) Next, this green sheet was dried at 80° C. for 5 hours, and was    subjected to punching to make portions for through holes 15 having    diameters of 1.8 mm, 3.0 mm and 5.0 mm, respectively, into which    silicon wafer lifter pins are inserted, and portions for conductor    filled through holes for connection to terminal pins.-   (3) Hundred parts by weight of tungsten carbide particles having an    average particle diameter of 1 μm, 3.0 parts by weight of an acrylic    binder, 3.5 parts by weight of α-terpineol solvent, and 0.3 part by    weight of a dispersant were mixed to prepare a conductor containing    paste A.

Hundred parts by weight of tungsten particles having an average particlediameter of 3 μm, 1.9 parts by weight of an acrylic binder, 3.7 parts byweight of α-terpineol solvent, and 0.2 part by weight of a dispersantwere mixed to prepare a conductor containing paste B.

The conductor containing paste A was printed on the green sheet byscreen printing, to form a conductor containing paste layer. The printedpattern was made to a pattern of concentric circles as shown in FIG. 2.The conductor containing paste B was filled into the through holes whichwould be conductor filled through holes for connection to terminal pins.

Thirty seven green sheets on which no tungsten paste was printed werestacked on the upper side (wafer-heating face) of the green sheetsubjected to the above-mentioned treatment, and 13 green sheets on whichno tungsten paste was printed were stacked on the lower side thereof,and then the green sheets were laminated at 130° C. and a pressure of 80MPa.

-   (4) Next, the resultant lamination was degreased at 600° C. in    nitrogen gas for 5 hours, and hot-pressed at 1890° C. and a pressure    of 15 MPa for 3 hours to obtain an aluminum nitride plate 3 mm in    thickness. This was cut out into a disc of 230 mm in diameter to    prepare a ceramic heater having therein heating elements having a    thickness of 6 μm and a width of 10 mm-   (5) Next, the plate obtained in the step (4) was grinded with    diamond grindstone, and then a mask was put thereon to make bottomed    holes 14 (diameter: 1.2 mm, and depth: 2.0 mm) for thermocouples in    the surface by blast treatment with SiC and the like.-   (6) Furthermore, a part of the through holes which would be    conductor filled through holes was hollowed out, and a gold solder    comprising Ni—Au was employed and heated for reflowing at 700° C.,    so as to connect terminal pins 13 made of Kovar to the concave    portions.

Regarding the connection of the terminal pins 13, a structure, wherein asupport of tungsten supports at three points, is desirable. This isbecause the reliability of the connection can be kept.

-   (8) Next, a pluralities of thermocouples 17 for temperature-control    were buried in the bottomed holes to finish the manufacture of the    ceramic heater 10.    (Example 4)    Control of the Temperature of a Ceramic Heater-   (1) A temperature-adjusting equipment (made by Omron Corp., E5ZE)    equipped with a control unit having a power source, a memory unit,    and an operation unit was prepared. Then, the wirings from the    control unit 43 were connected to the ceramic heater 30 (reference    to FIG. 3) manufactured in Example 1 through the terminal pins 13,    and a silicon wafer was put on this ceramic heater 30.

Incidentally, although not shown in FIG. 3, the bottomed holes 34 a to34 c are formed at the same position of the bottomed holes 14 a to 14 cof the ceramic heater 10 shown in FIG. 2. Also, the heating elements 32a to 32 c are formed at the same position of the heating elements 12 ato 12 c of the ceramic heater 10 shown in FIG. 2.

-   (2) Next, a voltage was applied to this ceramic heater 30, and the    temperature thereof was once raised to 200° C. Furthermore, the    temperature was further raised up to 200° C. to 400° C., and then    the temperature was measured with the thermocouples equipped in the    bottomed holes 34 a to 34 c. The measured results are shown in FIG.    4.

Profiles of electric powers (represented by current values) supplied tothe heating elements 32 a, 32 b and 32 c are shown in FIG. 5. In FIG. 4,the vertical axis represents temperature and the horizontal axisrepresents elapsing time. In FIG. 5, the vertical axis representscurrent value, and the horizontal axis represents time.

As obvious from FIG. 4, after the current started to be applied to theceramic heater 30, the temperature of the ceramic heater becomes even ina short period of time. As a result, the silicon wafer put on thisceramic heater 30 was not damaged in the process of the heating, and wasevenly heated.

Also, after heated up to 140° C., the state of recovery of thetemperature at the central portion, middle portion and peripheralportion of the ceramic heater 30, under such circumstance that thesilicon wafer of 25° C. is put thereon, was examined, and shown in FIG.8.

Also, as obvious from the result shown in FIG. 8, the temperature of theceramic heater 30 can be controlled to the original temperature insignificantly short period of time even if a disturbance is generated byabruptly putting a silicone wafer with low temperature thereon.

Also, when the similar temperature control is conducted by using theceramic heater obtained in the examples 2 and 3, the silicone wafer isevenly heated similarly to the above-mentioned case.

(Example 5)

The Temperature Control by the Thermoviewer

(1) A temperature-adjusting equipment (made by Omron Corp., E5ZE)equipped with a power source unit 630, a control unit 63, a memory unit61, and an operation unit 62 was prepared. Then, through the terminalpins 33, the wirings from the control unit 63 is connected to themanufactured heater plate 51 (ceramic heater 50, reference to FIG. 6)which had the similar structure to that of the case of Example 1 exceptthat the bottomed holes for inserting the thermocouples were not formedthreon. And then, the wiring from the thermoviewer 600 (made by JapanDatum Inc., IR162012-0012) was connected to the personal computer(FUJITSU Co.Ltd FM-V) which plays both roles of the memory unit 610 andthe operation unit 620.

The software for image processing (made by Cognex corporation)isinstalled in the personal computer. The image processing softwaresections the screen of the thermoviewer 600 into 10000 pixels, then thecolor of the sectioned pixels is subjected to the multi-level judgmentand valued in multiple steps of 0 to 9. When plural colors exist in thesection, the average value thereof is adopted. The average value of thetemperature controlled area is obtained from the figures thus obtainedby multi-level judgment. The temperature is determined from the colorcorresponding to the average value. Then, thus determined temperature ofrespective temperature controlled areas is transmitted to thetemperature-adjusting equipment.

(2) Next, a voltage was applied to this ceramic heater 50, and thetemperature thereof was once raised to 200° C. Profiles of electricpowers (represented by current values) supplied to the heating elements32 a, 32 b and 32 c are shown in FIG. 9. Further, the result of thetemperature measurement is shown in FIG. 10.

As obvious from FIG. 10, after the current started to be applied to theceramic heater 50, the temperature of the ceramic heater became even ina short period of time. As a result, the silicon wafer put on thisceramic heater 50 was not damaged in the process of the heating, and wasevenly heated.

INDUSTRIAL APPLICABILITY

As described above, according to the ceramic heaters of the presentinvention, by making the temperature of the wafer-heating face even, thewafer-heating face for an object to be heated can be made even, thewhole temperature of the object to be heated such as a semiconductorwafer and the like is made even, the damage of the semiconductor waferis prevented. Also, the temperature control can be successfullyconducted even in the case the unexpected temperature change occurs, andthus the present invention is significantly profitable.

1. A ceramic heater for heating a semiconductor wafer, comprising: aceramic substrate having a first surface and a second surface, the firstsurface being arranged as a heating face configured to heat thesemiconductor wafer; a resistance heating element formed on the secondsurface of said ceramic substrate or inside said ceramic substrate, andincluding at least two circuits; temperature-measuring means formeasuring a temperature of said ceramic substrate or a temperature ofthe semiconductor wafer; a control unit configured to supply electricpower to said resistance heating element; a memory unit configured tostore the temperature data measured by said temperature-measuring means;and an operation unit configured to calculate, based on said temperaturedata, electric power data required for said resistance heating elementto attain a uniform temperature of the heating face, wherein differentelectric power is supplied to each of the at least two circuits based onthe calculated electric power data.
 2. A ceramic heater for heating asemiconductor wafer, comprising: a ceramic substrate having a firstsurface and a second surface, the first surface being arranged as aheating face configured to heat the semiconductor wafer; a resistanceheating element formed on the second surface of said ceramic substrateor inside said ceramic substrate, and including at least two circuits;temperature-measuring means for measuring a temperature of said ceramicsubstrate or a temperature of the semiconductor wafer; a power sourceconfigured to supply electric power to said resistance heating element;a control unit configured to control the power source; a memory unitconfigured to store the temperature data measured by saidtemperature-measuring means; and means for calculating, based on saidtemperature data, electric power data required for said resistanceheating element to attain a uniform temperature of the first surface,wherein different electric power is supplied to each of the at least twocircuits based on the calculated electric power data.
 3. The ceramicheater for heating a semiconductor wafer according to claim 1, whereinsaid temperature-measuring means comprises a temperature-measuringelement.
 4. The ceramic heater for heating a semiconductor waferaccording to claim 1, wherein said temperature-measuring means comprisesa thermoviewer.
 5. The ceramic heater for heating a semiconductor waferaccording to claim 2, wherein said temperature-measuring means comprisesa temperature-measuring element.
 6. The ceramic heater for heating asemiconductor wafer according to claim 2, wherein saidtemperature-measuring means comprises a thermoviewer.
 7. The ceramicheater for heating a semiconductor wafer according to claim 1, whereinsaid ceramic substrate comprises a nitride ceramic or a carbide ceramic.8. The ceramic heater for heating a semiconductor wafer according toclaim 1, wherein said temperature-measuring means comprises athermocouple.
 9. The ceramic heater for heating a semiconductor waferaccording to claim 1, wherein said ceramic heater comprises pluraltemperature-measuring means.
 10. The ceramic heater for heating asemiconductor wafer according to claim 2, wherein said ceramic substratecomprises a nitride ceramic or a carbide ceramic.
 11. The ceramic heaterfor heating a semiconductor wafer according to claim 2, wherein saidtemperature-measuring means comprises a thermocouple.
 12. The ceramicheater for heating a semiconductor wafer according to claim 2, whereinsaid ceramic heater comprises plural temperature-measuring means. 13.The ceramic heater of claim 1, further comprising: a lifter pinconfigured to support the semiconductor wafer above and away from theheating face when the semiconductor wafer is heated by the heating face.14. The ceramic heater of claim 2, further comprising: means forsupporting the semiconductor wafer above and away from the heating facewhen the semiconductor wafer is heated by the heating face.
 15. A methodfor heating a semiconductor wafer, comprising: positioning thesemiconductor wafer above a ceramic substrate, the ceramic substratehaving a first surface and a second surface, and the first surface beingarranged as a heating face configured to heat the semiconductor wafer,heating the heating face with at least two heating circuits formed onthe second surface of the ceramic substrate or inside the ceramicsubstrate; heating the semiconductor wafer with the heating face;obtaining temperature data associated with a temperature of the ceramicsubstrate or a temperature of the semiconductor wafer; calculating,based on the temperature data, electric power data associated withattaining a uniform temperature of the heating face; and supplyingdifferent electric power to each of the at least two heating circuitsbased on the electric power data.
 16. The method of claim 15, wherein,the positioning includes supporting the semiconductor wafer at adistance above the heating face, and the heating of the semiconductorwafer includes heating the semiconductor wafer when the semiconductorwafer is supported at the distance above the heating face.
 17. Themethod of claim 15, wherein the obtaining includes measuring thetemperature of the ceramic substrate with at least one thermocouple. 18.The method of claim 15, wherein the obtaining includes opticallymeasuring the temperature of the semiconductor wafer.